The wakizashi was always carried along with the katana, to make a
daisho or pair. The wakizashi was, esentially, a shorter katana that
could be wielded with one hand. One of the main uses of the wakizashi
was to fight indoors, where the low ceilings of feudal japan would
make use of the long katana nearly impossible.
The katana-bearing samurai of the Genpei war period and the Warring
States Era would never leave behind their wakizashi, which was often
used as a backup weapon if the katana was lost or damaged. The wakizashi
came in handy when, at many times, the katana's length was a disadvantage.
The wakizashi was also used to perform seppuku, the ritual suicide of a member of the warrior class who felt he or she was living with great shame, from disappointing one's master or from being humiliated in a number of other ways.
The following description is graphic and certainly not for the squeamish. Please do not allow children to read it. The samurai, when asked to, or granted permission to, commit seppuku, would kneel in the traditional manner with his wakizashi at his side. He would take the short sword from it's saya and thrust it deeply into his own torso, cutting himself open vertically. He would then continue on his ritual, in spite of the pain, by cutting once more horizontally across the original wound. The samurai, having disemboweled himself, will have then died an honourable death. It was permissible to have a close friend or trusted ally to act as a second, meaning that he or she would stand behind the samurai and strike his head off with the katana after the first cut had been made. If a female samurai were to commit seppuku, she would only cut her own throat, a much simpler and cleaner ritual.